<form action="/admin/upload" method="POST" enctype="multipart/form-data">
    {{csrf_field()}}
    <select name="source_id">
        <option value="1">1</option>
        <option value="2">2</option>
        <option value="3">3</option>
        <option value="4">4</option>
    </select>
    <input type="file" name="file"/>

    <input type="submit" value="submit" />
</form>
